Electron gun having grid-accelerator
and grid-cathode insulator rod sup-
ports



June 28, 1966 R. C. PAULL 3,258,627

ELECTRON GUN HAVING GRID-ACCELERATOR AND GRID-GATHODE INSULATOR ROD SUPPORTS Filed NOV. 7, 1961 United States Patent 3,258,627 ELECTRON GUN HAVING GRID-ACCELERATOR AND GRID-CATHODE INSULATOR ROD SUP- PORTS Raymond C. Paul], Marion, Ind., assignor to Radio Corporation of America, a corporation of Delaware Filed Nov. 7, 1961, Ser. No. 150,799 5 Claims. (Cl. 313-82) This invention relates to electron guns for cathode ray tubes, and particularly to electron guns of the type in which a cathode and other electrodes are mounted in selected spaced relationship independently of each other on insulator rods disposed alongside the electrodes,

and to a method in the making of such guns of adjusting the spacing of the cathode from an adjacent electrode by use of capacitance measurement techniques.

Electron guns of this type wherein, e.'g., cathode, control, and accelerating electrodes are mounted adjacent to and independently of each other on the same insulator rod are highly desirable for some purposes. However, use of prior art capacitance measuring techniques has not been entirely satisfactory when applied to such guns of prior art design. The capacitance which gives the best indication of a desired condition of electrode relationships, e.g., spacings, is the very small capacitance that exists between the cathode and the accelerating electrode through the aperture of the control electrode. However, stray capacitance between the cathode and accelerating electrode in prior art guns having cathode, control electrode and accelerating electrode all directly mounted on insulator rods, is too great to permit an accurate determination of electrode spacing by measuring this small capacitance.

It is therefore an object of my invention to provide a new and improved electron gun structure of the general'type described above, Whose cathode-control electrode spacing can be accurately adjusted by means of a measurement of the capacitance between the cathode and the accelerating electrode.

It is also an object of my invention to provide a new and improved method of adjusting cathodecontrol electrode spacing by use of capacitance measuring techniques.

Briefly, according to one feature of my invention, in an electron gun including a cathode, a control electrode, and an accelerating electrode disposed adjacent to each other in spaced relation in the order named, the cathode and control electrode are secured independently of each other to a first insulator rod, and the accelerator electrode and control electrode are secured independently of each other to a second insulator rod spaced from the first rod. According to another feature of my invention at capacitance shield is inserted between the adjacent spaced ends of the first and second insulator rods, While the capacitance between the cathode and accelerating elec trode is being measured for the purpose of adjusting the cathode-control electrode spacing.

The single figure of the drawing is a longitudinal section view of an electron gun according to my invention.

In the drawing, an electron gun is shown to include a cathode electrode 1 2, a control, electrode 14, a screen or accelerating electrode 16, 1a first lens electrode 18, a focus electrode 20, and a second lens electrode 22. The electrodes .12 and 14 are mounted on, or secured to, a first pair of insulator support rods 24; the electrodes :14, 16, I18, and 22 are mounted on, or secured to, a second pair of insulator support rods 25. Each of the first pair of support rods 24 are preferably respectively coaxial with an axially spaced from one of the second pair of support rods 25. The control 3,258,627 Patented June 28, 1966 electrode 14 is thus secured to both the first rods 24 and the second rods 26 to unite the electrode assemblies into an integral structure, while at the same time providing a discontinuity of the insulator support rod means 24-25 between the cathode 12 and accelerating electrode 16. The purpose of this discontinuity is more fully described hereinafter.

The cathode 12 is closed at one end with a transverse wall 28 which is coated on the exterior surface with electron emissive material. The cathode 1-2 is mounted coaxially within a tubular cathode shield 30 .by a cathode support ring 32 disposed therebetween. The cathode and its associated shield and support ring are mounted on the first pair of support rods 24 by U-shaped mounting elements 34, the bights of which are welded to the shield 30, and the legs of which are anchored in the insulator rods 24. The emissive wall 28 of the cathode may be selectively spaced from the control electrode 14 such as, e.g., by a sliding of the cathode 12 within the ring 32 and/ or of the ring 32 within the shield 30 until finally positioned in its selected position, and then secured in place, e.g., by spot welding.

The control electrode 14 comprises a cylindrical wall 36 closed at one end with a centrally apentured end Wall 318. The bigh-ts of a pair of U-shaped mounting elements 40 are welded to the external surface of the cylindrical wall 36 of the control electrode 14. One leg of each of the elements 40 is anchored in one of the support rods 24; the other leg of each of the elements 40 is anchored in the support rods 25.

A coil heater 42 is disposed within the cathode 12 and is supported on a pair of straps 44 which are anchored in the first pair of insulator rods 24.

The accelerating electrode '16 is mounted .on the sec ond pair of insulator rods 25 by U-shape mounting elements 4 5, whose bights are Welded to the accelerating electrode "16, and whose legs are anchored in the support rods 25. The lens electrodes 18 and 22 and the focus electrode 20 are similarly mounted on the support rods 25.

A plurality of spring snubbers 46 are attached to a flange of the second lens electrode 22 and are adapted to support the gun 10 in the neck of a bulb into which it is ultimately incorporated.

A ring getter 47 is also mounted on the flange of the second lens electrode for gettering the tube into which the gun is incorporated.

As previously stated, in adjusting the spacing between the cathode 12 and the control electrode 14, it is preferred to sense the capacitance C between the cathode 12 and the accelerating electrode 16 and adjust the cathode position to provide a selected capacitance. Such a capacitance sensing takes into account possible minute variations in the size of the apertures in the control and accelerating electrodes 14 and 16 and the spacing between these electrodes.

However, in prior art guns having the cathode, control electrode and accelerating electrode mounted independently of each other on the same support rod, this preferred technique has been unsatisfactory. I have discovered that the reason is due to the excessive stray capacitance which exists between the cathode and accelerating electrodes through the common, continuous support rods on which these electrodes are mounted in these prior art guns. In the electron gun 10, the difl'iculty of stray capacitance is overcome by virtue of the discontinuity of the support rod mounting means, i.e., the use of a first pair of rods 24 on which the cathode 12 is mounted and which are separate from and spaced from a second pair of rods 25 on which the accelerating electrode is mounted.

The stray capacitance, which would otherwise exist through the support rods 24 and25, is even further reduced by insertion of metallic capacitance shields 48 between the adjacent spaced ends of the support rods 24 and 25, and by electrically connecting both the shields 48 and the control electrode 14 to the ground potential of the capacitance measuring apparatus. As a result, a measurement of capacitance C between the cathode 12 and the accelerating electrode 16 is indicative substantially of only that capacitance which exists between these electrodes through the central aperture of the control electrode 14.

The shield members 48 comprise conductive plates which preferably completely overlie the adjacent ends of the support rods 24 and 25 and thus capacitively shield them from each other. The shields may be provided as a permanent part of the electron gun 10, or may be a part of the capacitance measuring apparatus, and as such, removable frrom the gun after the spacing operation is complete.

What is claimed is:

1. An electron gun comprising a control electrode cup having a cylindrical side wall and a centrally apertured end Wall, a cathode extending into said cup and spaced adjacent to the internal surface of said apertured end wall, an accelerating electrode spaced adjacent to the external surface of said apertured end wall, a first pair of insulator rods each disposed alongside and fixed to said cathode and to the external surface of said cylindrical wall, and a second pair of insulator rods coaxial with and axially spaced from said first pair of insulator rods and each disposed alongside and fixed to said accelerating electrode and said external surface of said cylindrical wall.

2. An electron gun comprising a control electrode cup having a cylindrical side wall and a centrally apertured end wall, a cathode spaced adjacent to the internal surface of said apertured end wall, an accelerating electrode spaced adjacent to the external surface of said apertured end wall, a first insulator rod disposed alongside and fixed to said cathode and to the external surface of said cylindrical wall, and a second insulator rod coaxial with and axially spaced from said first insulator rod and disposed alongside and fixed to said accelerating electrode and said external surface of said cylindrical wall.

3. An electron gun including cathode, control, and accelerating electrodes disposed adjacent to each other in the order named, said control electrode comprising an apertured wall interposed between said cathode and accelerating electrodes, a first insulator support rod attached to said cathode and control electrodes and unattached to said accelerating electrode, thereby maintaining said cathode and control electrodes in fixed spaced relationship, and a second insulator support rod attached to said control and accelerating electrodes and unattached to said cathode electrode, thereby maintaining said control and accelerating electrodes in fixed spaced relationship.

4. An electron gun comprising a control electrode having an apertured wall, a cathode spaced adjacent to one surface of said apertured wall, an accelerating electrode spaced adjacent to the opposite surface of said apertured wall, a first insulator rod disposed alongside and fixed to said cathode and said control electrode, and a second insulator rod coaxial with and spaced from said first insulator rod and disposed alongside and fixed to said control electrode and said accelerating electrode.

5. An electron gun as in claim 4, further comprising a capacitance shield disposed between said insulator rods.

References Cited by the Examiner UNITED STATES PATENTS 2,163,210 6/1939 Wienecke. 2,174,853 10/1939 Bowie 2925.16 2,249,552 7/ 1941 Zworykin. 2,411,184 11/1946 Beggs 29-2516 2,633,553 3/1953 Ruska et al. 2,773,213 12/1956 Dodds. 2,840,739 6/ 1958 Lexovicz. 2,942,128 6/ 1960 Johnson.

GEORGE N. WESTBY, Primary Examiner.

R. SEGAL, Examiner.

C. O. GARDINER, Assistant Examiner. 

2. AN ELECTRON GUN COMPRISING A CONTROL ELECTRODE CUP HAVING AN CYLINDRICAL SIDE WALL AND CENTRALLY APERTURED END WALL, A CATHODE SPACED ADJACENT TO INTERNAL SURFACE OF SAID APERTURED END WALL, AN ACCELERATING ELECTRODE SPACED ADJACENT TO THE EXTERNAL SURFACE OF SAID APERTURED END WALL, A FIRST INSULATOR ROD DISPOSED ALONGSIDE AND FIXED TO SAID CATHODE AND TO THE EXTERNAL SURFACE OF SAID CYLINDRICAL WALL, AND A SECOND INSULATOR ROD COAXIAL WITH AND AXIALLY SPACED FROM SAID FIRST INSULATOR ROD AND DISPOSED ALONGSIDE AND FIXED TO SAID ACCELERATING ELECTRODE AND SAID EXTERNAL SURFACE OF SAID CYLINDRICAL WALL. 